Below the surface of Aotearoa New Zealand’s rivers swim numerous species of unique, mysterious fish. Today we’re zooming in on a precious, unusual, and poorly understood native freshwater fish, known around the country as lamprey, kanakana and piharau. We’ll take a look at a recent DOC survey aiming to track down where these elusive fish live, using some super sensitive technology.
Written by Sarah Wilcox.
A rather curious creature
Our native pouched lamprey is a treasured prehistoric species of fish. Other species have come and gone but lamprey were here 360 million years ago when dinosaurs inhabited the land and waters of Aotearoa.
This fish is a sucker-mouthed marvel. It’s secretive, has strange eating and reproductive habits, and is a stand-out rock climber. But we’ll get to all that later.
Once a mighty food resource
Lamprey used to be plentiful across the country, and there are stories of massive harvests in the past. They remain a taonga and mahinga kai species but now have a conservation status of Threatened – Nationally Vulnerable, so are in quite a bit of trouble here.
As a first step to securing populations of these remarkable fish, we’ve been finding out where they are. Once we know that, we can work to protect them and the habitats they need to complete their lifecycle.
Buried babies, blue adults and underwater nests
Anna Henderson is a DOC freshwater ranger from Marlborough. She’s only seen lamprey a few times in her career but is fascinated by the species.
“They’re really different from our other native fish. Like whitebait, lamprey migrate up and down streams, and spend some of their lives at sea. While at sea they are parasitic – they suck onto fish, sharks and whales and slurp their blood and body fluids for food.”
Once they’ve grown into sleek blue adults with racing stripes, lamprey return to our rivers and head upstream – sometimes travelling more than 100 kilometres. Here, they give up their blood-sucking ways and don’t eat anything for a full 12–18 months. They tend to hide during the day under logs or large rocks, or burrow into streambeds.
Male and females get together in rivers and tributary streams, where they lay and fertilise their eggs in a rocky cavity or ‘nest’. Then they die, job done.
As a summer student, Anna was lucky enough to see the first documented lamprey eggs in the Southern Hemisphere.
“They were in a nest being guarded by the dad. That was only in 2013, so it shows how recent this kind of knowledge about them is.”
Once hatched, the larvae move downstream and burrow into river sand. Here they stay, feeding while under the sand and emerging at night to filter-feed on passing algae and microorganisms. After 3–4 years, they have become juvenile fish that measure 80–120mm long.
“Another big moment for me was on a training exercise in Pollard Park in the middle of Blenheim. We were testing out our electric fishing methods. After 4 minutes we’d almost given up hope of finding any juvenile lamprey, but then they came wriggling up out of the sand, coaxed by the tingling from the machine. What a huge surprise that was!”
Sniffing them out with clever science
The partially buried larvae give off tiny amounts of a pheromone called petromyzonol sulphate while they’re feeding. This is one of several chemicals that guide adult fish as they swim upstream, signalling places with good habitat for breeding and for juvenile fish to grow.
Thanks to some clever science, the presence of this pheromone can also tell us if there are young fish in a stream. Dr Cindy Baker, NIWA Principal Scientist, has developed a method to detect it, even in miniscule amounts.
“We can detect the chemical in the femtomolar range, which is a concentration of around 5g (one teaspoon) in 580,000 Olympic-sized swimming pools!”
The detection method involves immersing a small sampler (essentially an absorbent bag) in the middle of a stream and leaving it there for 3 weeks. During this time the sampler accumulates molecules of pheromone from the water flowing over it. The samplers are then collected, put on ice and sent back to the lab where Cindy extracts out the pheromone and determines the amount present.
These monitors can identify the most popular streams (high levels of pheromone), the least popular (low levels of pheromone) and the streams with few or no lamprey present (no pheromone detected). Other methods like eDNA can only tell us if lamprey are present or not.
“We checked the influence of the pheromone by microchipping adult lamprey and tracking their movements. Their stream choice matched the level of pheromone we detected with the samplers.”
Cindy says the method has to be exquisitely sensitive to detect pheromone at those concentrations.
“The levels we’re measuring say a lot about the lamprey’s powerful sense of smell. But we believe they can smell even lower concentrations than we can detect with the latest machines.”
Sampling sites in Marlborough
Anna and her team put pheromone samplers in several local rivers in February. She placed 20 in likely spots, based on anecdotal evidence, environmental DNA testing and previous electric fishing.
“The samplers have to sit in the main water flow and stay covered for the whole time, so we hoped they wouldn’t dry out, be destroyed by floods or get tangled up with debris. It was a nervous wait!”
Fortunately the weather was kind and Anna got some great results.
“I really didn’t know what to expect, so all the results were interesting and surprising. In the Ōhinemahuta (Onamalutu) River, every sampler except one picked up pheromone even though the levels varied quite a bit. Overall, it was a real success and has given us lots of leads to follow up on.”
Anna’s freshwater ranger colleagues around the country surveyed their local areas, covering streams in Nelson, Motueka, West Coast, Otago, Canterbury, Wairarapa and Taranaki. (It wasn’t an exhaustive survey of the country.)
The results from DOC’s survey work to date are shown on the maps. To protect the fish the exact locations have not been shown. The highest levels were from especially favourable streams in Otago and on the West Coast.
The bigger the green circle, the higher the concentration of pheromone in the waterway. The largest green circles indicate very high (>100 femtomolar) concentration of pheromone, with the smallest green circles indicate low (12–30 femtomolar) concentration of pheromone. Orange dots indicate that no pheromone was detected at the site.
Lamprey pheromone results from North and South Islands.
(Click on the map to see a larger image).
Treasuring this taonga species for future generations
For Māori, lamprey is a prized delicacy and taonga species. Our work is building strong links with local mana whenua to ensure populations of the species are secured around the country. We’re also keen to connect with other landowners who are lucky enough to have a lamprey hotspot on their property.
“Last summer’s work was a first attempt – and quite exploratory. We’re keen to expand on what we did, get more detailed information and follow up where there were failures”, says Anna.
“As we carry on our surveys, we’ll learn more about what would benefit the species most. It may be that as they go upstream, they reach barriers like weirs that they can’t climb, and these stop their movement. Or it could be that gravel extraction or river modification work is degrading the sandy areas that the young fish need. Another issue could be water quality or sediment filling up the rocky nesting spots.”
Anna says the work will help inform future restoration activities.
“If no one knows they’re there, they can’t be protected. As we build up knowledge about where they are, we can work to get protection in place. It’s so interesting working on a species that we know so little about.”
Cindy agrees. “It’s exciting to see the tools NIWA has developed being used for the conservation of such an enigmatic and special species.”
Facts about the strange and wonderful lamprey
Lamprey have no jaws and no bones, just a circular mouth full of rasping teeth. The suction mouth allows them to climb rocks and waterfalls, and latch on to whales, sharks and other fish while at sea.
There are around 44 species of lamprey known worldwide but only two are known to climb waterfalls with their bodies completely out of the water. This is our pouched lamprey (Geotria australis) and the Pacific lamprey (Entosphenus tridentatus). (*Cheering*)
Lamprey may attach themselves to their host fish for days or weeks at a time, and they leave tell-tale circular scars. Like mosquitos, lamprey release an anticoagulant into the host fish to keep the juices flowing.
The life stages of lamprey are so different that biologists in the 19th century thought each stage was a distinct species of fish.
Pouched lamprey get their name from the flabby pouch that males grow under their mouths before spawning. Its purpose is still unknown.
Threatened Pacific lamprey have been encouraged entry and to re-colonise the Columbia River in western Canada by rearing larvae and introducing them into streams. Here the larvae release the pheromone that guides adults to return from the sea.
Māori used utu piharau or pā kanakana (lamprey weirs) to harvest the species. The weirs forced fish to swim between gaps in a wooden barrier into a hinaki (eel trap). Utu piharau were once common on the Whanganui River.
In the past, lamprey were harvested in huge number. In 1918 a writer described a night’s fishing on the Waitara River in Taranaki, in these words, “…for a single night’s netting during a fresh in June, three sacks were filled—probably between two and three thousand.”
Our pouched lamprey is found throughout Aotearoa including the Chatham Islands and Stewart Island/Rakiura. It’s also widespread in the Southern Hemisphere including Australia.